At the molecular level, networks are given by multiple interaction of nucleic acids and proteins and by protein-protein interactions. The latter results, for the most part, in formation of multiple protein complexes (MPCs). My research group is interested in studying an MPC formed by components involved in important DNA transactions when cells are exposed to DNA damage. This is a condition that induces the expression of error- prone DNA polymerases, the activity of which might lead to mutations. Our long-term goal is to learn about the mechanisms that regulate the activity of error-prone Y-family DNA polymerases. This will provide a detailed understanding of the mutation pathways in bacteria. In turn, this will lead to a good understanding of the involvement of error prone Y-family DNA polymerases in the evolution of important functions such as antibiotic resistance. Importantly, this project will contribute to the general understanding of mutagenesis, since Y-family polymerases are conserved from bacteria to humans. Bacteria and especially the model system Escherichia coli is perfect to study and ask questions regarding basic conserved biological processes such as those generating mutations, especially in cells under stress. Due to its relative simplicity, studying basic processes in bacteria will render mechanistic insights that would be difficult to attain directly in more complex systems. We propose in this application that protein-protein interactions, and likely MPC formation, modulate the activity of Y-family DNA polymerases allowing to sculpt mutagenesis that might permit survival in conditions of stress. During this research, we will address questions of whether the MPC that we analyzed with purified components display similar features in living cells. Understanding how to control the activity of error-prone DNA polymerases has far reaching implications due to their evolutionary conservation. Therefore, any insights learned during this research can be translated to understand the control of these activities in other cellular systems. Moreover, learning about the functionality and modes of formation of MPCs will allow us to gain insights into the biological rules governing these protein machines, and thus learn how to manipulate them to our advantage.